An Anthem spokesman said the company has offered the affected doctors free credit monitoring and credit insurance.

Like many insurers, Anthem has been revamping its provider directory for consumers to reflect changing networks of doctors and hospitals for new policies being offered under the federal healthcare law.

If tax identification or Social Security numbers fall into the wrong hands, they can often be used to file bogus medical claims with insurers and government agencies such as Medicare.

Federal investigators have been trying to clamp down on Medicare billing fraud in recent years, particularly in hot spots such as Southern California.